Self-help books that helped you during rock bottom moments?

I've been diagnosed with MDD since I was a teenager, and the last few years have been just a big blur. Recently, I finally broke through my brain fog and suddenly had an urge to do things to help myself. I've been a reader for so long (it's my escape), but mostly fiction. I thought I'd ask for recommendations for self-help books this time, books that you've proven and tested helped you (not that I fully expect them to help me too, I just want to take a gamble with an open mind). TIA!